Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more electric motors coupled to one or more high performance centrifugal pumps. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment.
Like conventional motors, submersible motors typically operate by using a “stator” to create a series of moving electromagnetic fields that cause a ferromagnetic “rotor” to spin about a fixed axis. In submersible motors, the stators usually surround the rotors, which are secured to a center shaft that is used to transfer the output of the motor. In this way, the rotor and shaft spin about a common axis inside the motionless stator.
Submersible motors can vary in length from a few feet to nearly one hundred feet and may be rated up to hundreds of horsepower. In longer submersible motors, it may be desirable to employ a number of separate rotor sections within a single stator. Each rotor section is usually constructed from a number of thin pieces of material, or laminations, that are held in place by electrically conductive rods inserted through openings in the laminations. The shaft can be secured within the inner diameter of the rotor sections with a keyed connection or by one of several other well-known methods.
Bearing assemblies are typically placed between adjacent rotor sections to center the rotor and shaft within the stator. Most rotor bearing assemblies include a bearing sleeve that rotates in close proximity with a surrounding bearing collar. The bearing sleeve is typically fixed to the motor's shaft and the bearing collar is fixed in a stationary condition to the stator. In most submersible motors, the rotor bearing assemblies are “hydrodynamic,” and rely on the presence of a thin film of lubricant in the annulus between the bearing sleeve and bearing collar.
In some prior art designs, lubricant is pumped into the annulus between the bearing sleeve and bearing collar by the centrifugal force generated by the spinning shaft and bearing sleeve and shaft. Lubricant is supplied to the bearing sleeve through a hollow channel in the motor shaft that is connected to a lubricant reservoir. Linearly aligned ports in the shaft and bearing sleeve deliver the lubricant from the hollow channel in the shaft to the annulus between the bearing sleeve and collar. The lubricant then flows into the spaces between the rotor sections and the stator, thereby protecting these components.
By way of illustration, FIG. 1 shows a prior art rotor bearing assembly 200 includes a rotor bearing sleeve 202 that is secured to a hollow shaft 204 and a rotor bearing collar 206 that is attached to the stator 208. The rotor bearing sleeve 202 may be secured to the shaft 204 and the bearing collar 206 to the stator 208 by any of a number of well known methods, such as keyed connections 210 and 212. An oil-filled annulus 214 occupies the space between the bearing sleeve 202 and bearing collar 206. As the bearing sleeve 202 and shaft 204 rotate, lubricant is drawn out of the shaft 204 and pushed into the annulus 214 through a port 216. In this way, the bearing sleeve 202 propels lubricant from the shaft 204 into the annulus 214 through the port 216.
As motors continue to increase in speed and power, the need for effective lubrication also increases. Although effective to a limited degree, prior art rotor bearings fail to circulate sufficient quantities of lubricant to satisfy the demands of next generation motors. Without sufficient lubrication, the moving components of the submersible motor can become worn and result in mechanical or electrical failure. Failure of the components in the motor can result in expensive repairs and work stoppages. Cost savings can be realized with motors that last longer and incur minimal downtime.
There is therefore a continued need for improving the lubrication of submersible motors. It is to these and other deficiencies in the prior art that the present invention is directed.